Heat treating process for aluminum base alloys containing tin



May 10, 1966 HEAT TREAIING PROCESS FOR ALUMINUM BASE ALLOYS CONTAININGTIN Original Filed Aug. 2'7, 1963 INVENTORS M/CHAEL J PPYOR DOUGLAS 8.K57)? PHIL/P R. SPERRV AT TORNE V J. PRYOR ETAL 3,250,649

United States Patent 1 Claim. ((31.148-13) This is a division ofapplication Serial No. 304,923, filed August 27, 1963, which is acontinuation-in-part of applications Serial No. 60,166, filed October 3,1960, now Patent No. 3,180,728, Serial No. 171,114, filed February 5,1962, now Patent No. 3,186,836, and Serial No. 251,024, filed January14, 1963, now Patent No. 3,189,486.

The present invention relates to primary cells of the dry" type, andmore particularly, to an aluminum base alloy as an anode thereof, saidanode also serving as the container for the cell.

The metal zinc is extensively employed as anode in the construction ofdry cells, for example, flashlight batteries. Numerous proposals havebeen made heretofore to substitute aluminum for zinc as the anodematerial in order to utilize the numerous advantageous properties of thealuminum, for example, aluminum generally attains a higher anodicefiiciency than zinc, and has much higher coulombic output per unit massof anode metal consumed. In addition, aluminum enjoys a greater ease offabrication to thin gauge and to formed dry cell battery cases. Stillfurther, aluminum has a generally higher corrosion resistance when thebattery is on open circuit.

Dry cells containing aluminum, aluminum-zinc alloys or aluminum basealloys in general as the anode material have, however, suffered fromnumerous significant disadvantages, for example, such cells generallyrequire a considerable elapsed time for the cell current to reach itssteady maximum value, especially if the cell is kept on the shelf forextended periods of time. This elapsed time prevents the highlydesirablequick response for current when the cell is placed in a circuit.Inaddition, aluminum and aluminium base alloys generally sufier fromperforation of the cell wall either during service or during storage if,for example, the common halides are used as the electrolyte.Furthermore, composite alloys utilized to overcome the foregoingdisadvantages are not entirely satisfactory and are more expensive.

It is therefore an object of the present invention to provide animproved primary cell of the dry type.

It is a further object of the present invention to provide an improvedprimary cell as above utilizing an aluminum base alloy as the anodewhich also serves as the container for the cell.

It is a further object of the present invention to provide a primarycell of the dry type as above which enjoys the natural benefits ofaluminum as the anode material while overcoming the heretofore suffereddisadvantages in the use of this material.

It is an additional object of the present invention to provide a primarycell which is capable of galvanic currents of the same order ofmagnitude as those produced by zinc and which is also capable of highergalvanic currents, if desired.

It is a further object of the present invention to provide a primarycell of the dry type as above which is capable of quick response forcurrent when placed in the circuit despite extended storage periods andalso which does not suffer perforation of the cell wall during storageor during service.

3,250,549 Patented May 10, 1966 Further objects and advantages willappear hereinafter.

The figure is a diagrammatic view, partly in section, illustrating a drycell structure embodying the present invention.

In accordance with the present invention it has now been found that theforegoing objects and advantages may be readily accomplished and aprimary cell of the dry type obtained, said cell comprising a cathode,preferably a conventional cathodic depolarizer, an electrolyte and analuminum base alloy container as the anode, said alloy containing atleast percent aluminum and between 0.01 and 0.5 percent tin, wherein thetin is preferably retained in solid solution in an amount of from 0.01to 0.06 percent.

The improved aluminum base alloy of the present invention contains tinin an amount from 0.01 to 0.5 percent and at least 90.0 percentaluminum, and preferably at least percent aluminum. The tin is retainedin solid solution to the minimum degree, i.e., only in sufficient amountto yield the desired range of current density and preferably in therange of 0.02 to 0.05 percent, with the excess tin, or a suitable thirdingredient being provided as taught in the above-identified co-pendingapplication S.N. 60,166, now Patent No. 3,180,728, to improve uniformityof corrosion and to improve anodic efficiency.

The preferred manner of preparing this alloy is to heat an aluminum tinalloy containing from 0.04 to 0.5 percent tin at a temperature from to540 C. In this temperature range the solid solubility of tin in aluminumis from about 0.05 to less than 0.02 percent. The time or heating is fora sufficient period of time to precipitate any excess tin from solidsolution and to develop the particulate form which produces maximumuniformity of attack and power eficiency. Generally, the heating periodWithin the preferred temperature range is at least 15 minutes and mayvary between 15 minutes and 48 hours. Longer times may be used but noparticular advantage is thereby obtained. After the heating period, thesample may be cooled rapidly or slowly. For simplicity, this treatmentmay be termed heterogenization treatment.

If desired, the heterogenization treatment may be combined withfabrication procedures, such as hot Working or annealing.

The heterogenization treatment may be preceded by a homogenizationtreatment, described in detail in copending application Serial No.60,166, now Patent No. 3,180,728. The homogenization treatment isintended to retain the maximum amount of tin in solid solution, i.e., upto 0.1 percent, by heating at a temperature of around 620 C.- *-20 C.and then rapidly cooling. The homogenization treatment also serves togive a uniform distribution of the tin throughout the alloy. Theheterogenization treatment which follows serves to reduce the tin insolid solution to levels acceptable for the dry cell application.

In accordance with the present invention it has been found that byutilizing the aluminum base alloy of the present invention as the anode,that is, as the cell container, a greatly improved dry cell is obtained.

The alloy of the present invention contains from 0.01 to 0.5 percenttin. The preferred tin content varies with the means used for control ofthe amount of tin remaining in solid solution within the broad limits of0.01 to 0.06 percent. If no heterogenizing treatment is to be used, thepreferred tin content is from 0.01 to 0.06 percent. Alternatively, thepreferred tin content in solid solution may be maintained by the use ofother alloying additions which serve to reduce the solid solubility oftin in aluminum, i.e., no heterogenizing treatment may be used andamounts of tin in excess of 0.06 percent employed while purity aluminumis much less economical than commercial and lower purity compositionswhich generally fulfill the same requirements. Therefore, it ispreferred in the present invention to utilize lower purity aluminum,i.e., an alloy containing from 0.001 to 0.05 percent silicon and fromabout 0.001 .to 0.1 per-cent iron. This lower purity composition may besubstituted for the high purity one without detriment to theelectrochemical characteristics.

It should be further understood that the alloy of the present inventionmay contain in addition to the aluminum and tin and the impurities,other metal components. These additional components may be added toachieve particularly desirable results.

' Generally, insoluble elements may be added to the alloy, i.e.,elements which have less than 0.03 percent solid solubility in aluminumat 620 C. The total amount of these insoluble elements should preferablybe no greater than 0.5 percent. Examples are iron, nickel and cobalt.These insoluble elements have very little or no significant efiect oncurrent output as they do not reduce the solid solubility of tin inaluminum, but they act as second phase particulate cathodes and largeamounts ultimately reduce anodic efficiency by promoting local corrosionof the anode.

Soluble elements may be also added to the alloy, i.e., elements'whichhave greater than 0.03 percent solid solubility in aluminum. The solubleelements may be considered either lattice expanders or latticecontractors, i.e., ternary addition elements which either expand orcontract the aluminum lattice. Generally the lattice expanders stabilizetin in retained solid solution and permit high galvanic currents to bedrawn from the alloy. Therefore,

since it is necessary to moderate the high galvanic current of the alloyof the present invention when it is utilized as the anode for a drycell, it is not desirable to utilize large amounts of lattice expandersunless they are required for other purposes, such as strengthening thealloy, improving the castability or increasing galvanic efficiency, inwhich case their effect upon galvanic current may be counteracted byheterogenization treatment or by other alloying additions. Typicallattice expanders include, for example, magnesium, zirconium, gallium,bismuth and indium. Only small amounts of these materials should beused.

Lattice contractors generally reject tin from solid solution and have amoderating effect on the galvanic current. Therefore, it is desirable toutilize these lattice contractors, especially where no heterogenizationtreatment is used and tin in excess of 0.06 is used. Naturally, theamount of lattice contractor will vary in each particular case, butgenerally in an amount from 0.005 to 4 percent is used. Typical latticecontractors and representative amounts thereof include, for example,zinc from about 0.01 to 1 percent, copper from about 0.01 to 1 percent,silicon from about 0.01 to 1 percent, manganese from about 0.01 to 1percent, silver from 0.01 to 1 percent and mixtures thereof.

Those elements most elfective in moderating overly aggressive cellcurrents and preferred amounts thereof are: silver in at least 0.1percent; zinc is at least 0.02 percent; copper in at least'0.0l percent;and silicon in at least 0.1 percent.

Any suit-able cathode may be employed in the dry cell of the presentinvention, for example, the conventional carbon or graphite cathodes maybe utilized. These are usually used with a conventional cathodicdepolarizer, such as manganese dioxide.

The various electrolytes suggested in the art for use in dry cells maybe conveniently used in the primary cell of .the present invention, forexample, the chloride paste electrolytes conventionally used in drycells are perfectly g suited for use in combination with the aluminumbase alloy of the present invention. The chloride paste'electrolyteswhen utilized in the dry cell of the present invention surprisingly donot result in perforation of the cell wall either during service orduring storage. This is a significant advance of the present invention.

Referring to the figure, which illustrates an embodiment of the presentinvention, outer shell -1, which is the aluminum-tin alloy of thepresent invention is lined with an inert, permeable, porous separator 2,the top edge of which may be crimped inwardly to assist in retaining thepaste in position. The porous layer serves to prevent direct contact ofthe mix with the shell yet is permeable to the. electrolyte. Aconventional carbon rod 3 centrally disposed in the shell is thecathode. Between the .porous separator and the carbon rod is the paste 4containing the electrolyte, depolarizer, and finely divided carbon.Above the paste is a space 5 which can accommodate any expansion of thepaste that may occur without rupturing the cell wall or top seal. Thecell is sealed by a suitable plastic or resinous substance 6 inassociation with a fibrous separator 7. The carbon rod 3 is providedwith a conventional metal cap 8 to insure good electrical contact withanother metallic conductor.

It is a further significant advantage of the present invention that whenthe alloy of the present invention is utilized for the anode material itis unnecessary to employ composite container materials to overcome thedisadvantages of perforation of the cell container by localizedcorrosion.

These composite container materials have been frequently employedheretofore in order to enable the use of an aluminum alloy as the anode.It is highly desirable to avoid the use of these composite materialsespecially because of the added cost of manufacture and still attain theadvantages rendered therein. It has been found in accordance with thepresent invention that it is unnecessary to utilize composite containermaterials view of the surprising advantages inherent in the aluminumbase alloy of the present invention.

The present invention and the improvements attained thereby will be morereadily apparent from a consideration of the following illustrativeexamples.

Example 1 This example describes representative preparation of aluminumalloys with tin contents of 0.02, 0.04, 0.08, 0.12 and 0.20 percent. Thealuminum used was at least 99.995% pure to which pure tin was added andstirred in while the aluminum was in the molten condition. Each alloywas cast into a rectangular steel mold coated on the inside with purelime.

In this example, a block, 3 x 3 x 0.85 inch was cut from each ingotafter the ingots had been homogenization heat treated for r16 hours at620 C. and cooled in air. Each block was alternately cold rolled to givereductions in thickness of about 35 percent, followed by intermediateannealing for one hour at 500 C., until a final thickness of 0.060 inchwas reached. Final heat treatment consisted of heating at 620 C. for 8hours, quenching in water, and heterogenizing by subsequent heating at400 C. for 24 hours and quenching in water. For each of these alloys thetin content in solid solution was in the range of 0.01 to 0.06 percent.t

The above example describes only one of many fabrication sequences whichhave been success-fully used to produce rolled sheet, including the useof hot rolling to Example 2 A test cell was prepared in order to testthe galvanic characteristics of the foregoing alloys. The cell usedconsisted of 10 square cm. of surface area of the desired aluminum alloyas anode and an equal area of steel his cathode, with a 0.1 N sodiumchloride electrolyte, as described in an article in the Journal of theElectrochemical Society, volume 105, No. 11, starting at page 629 andalso as described in co-pending patent applications Serial No. 60,166,now Patent No. 3,180,728, Serial No. 171,114, now Patent No. 3,186,836,and Serial No. 251,024, new Patent No. 3,189,486, above-identified. Thisrepresentative cell demonstrates the dry cell behavior to be expected ofthe anode alloy in a wide variety of chloride electrolytes.

Example 3 A test cell was set up in accordance with Example 2 utilizingthe alloys prepared in Example 1. The cell with these alloys began toproduce a current as soon as the external circuit was closed. Also,dissolution of the rolled anode alloys according to this inventionoccurred uniformly over the surface during the period of operation ofthe cell, and there was negligible local corrosion of the anode alloysduring periods of open circuit. Comparative-ly, an aluminum-one percentzinc alloy failed to produce current as soon as the external circuit wasclosed, did not dissolve uniformly and attained significant localcorrosion.

Example 4 A dry cell was prepared in a manner after the figure using analuminum-tin alloy containing 0.12 percent tin and normal iron andsilicon impurities. The alloy was prepared in accordance with theteachings of Example 1 to insure the tin in solid solution in thepreferred range. The same excellent results were obtained as in Example3.

Example 5 This example illustrates the use of an impurity element or anintentionally added alloying element to moderate the current output. Inthis case, aluminum alloys containing 0.12 percent tin and about 0.05percent iron with the moderating element silicon varying in the range of0.05 to 0.30 percent. Within this range, upon setting up the test cellof Example 2, the number of coulo'mlbs passed in 48 hours declined from500 at the lowest silicon content to 30 at the highest silicon content.All alloys had first been homogenized to place the maximum amount of tinin solid solution. Thus, it was proved that a low level of currentoutput, suitable .for use in a dry cell circuit, can be obtained bysuitable choice of a third element in the aluminum-tin alloy. A furtherdemonstration of this effect was found in a high purity alutminu.m0.20percent tin alloy with silver additions in the range of 0.01 to 0.09percent. At the lowest silver content the 6011101111138 passed in 48hours amounted to 1000, whereas, at the highest silver content it wasreduced to 100.

This invention may be embodied in other forms or carried out in otherways without departing from the spirit or essential characteristicsthereof. The present embodiment is therefore to be considered as in allrespects illustrative and not restrictive, the scope of the inventionbeing indicated by the .appended claim, and all changes which comewithin the meaning and range of equivalency are intended to be embracedtherein.

What is claimed is:

A process for preparing an aluminum \base alloy containing at least '90percent aluminum and from 0.04 to 0.5 percent tin, wherein the tin isretained in solid solution in an amount from 0.01 to 0.06- percent,which comprises: heating an aluminum base alloy containing from 0.04 to0.5 percent tin at a temperature from 150* to 540 C. for at least 15minutes.

References Cited by the Examiner UNITED STATES PATENTS 1,629,699 5/ 1927Guertler et a1 14*8159 2,087,992 7/1937 Nock 14 8-159 2,225,925 12/ 1940Nook 148-432 2,886,432 5/1959 Schmitt et al. 7'51 3 8 3,063,832 11/1962Snyder '-13'8 HYLAND BIZOT, Primary Examiner. DAVID L. RECK, Examiner.

R. O. DEAN, Assistant Examiner.

0.04 TO 0.5 PERCENT TIN AT A TEMPERATURE FROM 150 TO 540*C. FOR AT LEAST15 MINUTES.